Although there is evidence of the mechanisms used by both
strains when inoculated individually, there is no evidence of the
mechanisms used upon combination. An attempt to unravel the
mechanisms involved in effects of the combination can be done
based on data of AUDPC in 2006 (Fig. 6). The most effective
treatment was treating rice plants with the combination of the
two PGPR on leaves in three physiological stages irrespective of
disease severity, suggesting a biocontrol mechanism, which has
been demonstrated before for these strains in tomato and pepper
(Domenech et al., 2006). However, a single seed treatment was
able to reduce disease severity in almost 50%, suggesting in this
case induction of systemic resistance, because bacteria would
colonize the root upon germination, causing a systemic activation
of defensive mechanisms, that is, priming the plant for subsequent
pathogen attacks. Finally, treating plants on leaves either
one dose combined with the chemical treatment, or leaf
treatments in three phenological stages, was more effective than
seed treatment alone, suggesting that both mechanisms can be
working at the same time.